Filter housings equipped with several filter elements such as filter cartridges or wound modules are used, for example, for pressure filtration of fluids such as liquids and gases for separation of undesirable components such as heavy metal ions, microorganisms from waste water or beverages, for the concentration of proteins, for sterile filtration in the pharmaceutical industry, and so forth. Such filter elements are subjected to mechanical loads during both filtration and filter cleaning. The bending or warping of plastic filter elements in their longitudinal axis has a particularly serious effect in that it results in damage to the filter elements, including the filter materials, rendering them unusable. Such warping is caused primarily by flow turbulence, by pressure surges, and by backflushing.
Attempts to prevent such warping of the filter elements by means of locking devices is known. For example, Soviet Union Patent No. 17 54 157 Al discloses a multiple filter housing with several filter elements that are accommodated on the permeate side by a base plate. Above the filter elements on the feed side there is a plate-shaped contact pressure device through which adjusting screws are inserted to the end caps of the filter elements in order to lock them in place. The plate-shaped contact pressure device is attached to a central spacer rod. With this locking device, differences in the overall heights of the filter elements can also be accommodated on an individual basis by the adjusting screws. However, a major drawback to such an arrangement is that the filter elements cannot expand along their length at varying elevated temperatures such as are encountered with inline superheated steam sterilization, which can still lead to warping damage of the filter elements. Other drawbacks of this arrangement are that the locking device consists of many components, which makes assembly and disassembly of the filtering apparatus very time-consuming, and that the multiple components have numerous edges and cavities that are difficult to clean. Moreover, such a design does not comply with generally accepted regulations of the U.S. Food and Drug Administration (FDA), does not comply with FDA Good Manufacturing Practices and generally does not provide a satisfactory technical solution.
It is therefore a principal object of the invention to provide a multiple filter apparatus with a locking device for filter elements from a minimal number of components whereby bending or warping of the filter elements is prevented, differences in the length of the filter elements caused by manufacturing tolerances are tolerated, and thermal expansion and contraction of the filter elements is permitted. Another object of the invention is to provide a multiple filter apparatus with a locking device that is simply constructed and easy to lock, and that has a minimal number of parts that are difficult to clean.
These objects and others which will become apparent to one of ordinary skill in the art are provided by the present invention, which is summarized and described in detail below.
The invention comprises a multiple filter housing consisting of a housing dome and a housing base with a base plate, the housing being equipped with a locking device consisting of a spacer rod and a centering plate. The housing is provided with connections for the feed and discharge of fluids and accepts a number of cartridge-type filter elements, such as filter cartridges or spiral wound modules, that are accommodated and affixed to the base plate in conventional fashion so as to divide the feed and permeate zones, whereby the fluid to be filtered proceeds from one zone to the other only through the filter material of the filter elements by the application of a pressure difference between the feed and permeate zones. The filter elements have guide adapters on their ends distal to the base plate which have a smaller diameter than the overall diameter of the filter elements themselves and that usually taper at the top. The multiple filter housing can be operated in any position, but is preferably operated so that the filter elements stand upright, i.e., the guide adapters point upward.